Nacelle Cover for a Wind Turbine

ABSTRACT

A nacelle cover (240) for a wind turbine including a composite material elongate housing (245) defining an interior space for containing machinery components of the wind turbine, the housing (245) having a front end (247) for mounting to a tower (252) of the wind turbine, and an opposite rear end (248). At least one machinery component (125) of the wind turbine is mounted on the housing (245) at a position laterally spaced from the tower (252) in a longitudinal direction along the housing (245). The housing (245) includes a structural tube (242) which functions as a vertically displaceable cantilever beam carrying the load of the at least one machinery component (125) mounted thereon. In an unloaded state prior to mounting the at least one machinery component (125) on the housing (245), the rear end (248) is higher than the front end (247), and in a loaded state after mounting the at least one machinery component (125) on the housing (245), the rear end (248) is lowered as compared to the unloaded state by flexural elastic deformation of the structural tube (242).

FIELD OF THE INVENTION

The present invention relates to a nacelle cover for a wind turbine.

BACKGROUND

A wind turbine converts the kinetic energy in the wind into mechanicalpower by means of a rotor coupled to main machinery components. Windturbines comes in various sizes ranging from small wind turbines to verylarge turbines, the majority of which are large three-bladedhorizontal-axis wind turbines (HAWT). The large wind turbines are highand have a very large numbers of main machinery component groups andsubcomponents installed on a frame inside the nacelle cover. Windturbines from different manufacturers have different frames andarrangements of machinery to fit inside the various designs of compositenacelle cover, which designs have an impact on the arrangement of themachinery as well.

One of the largest components located inside the nacelle cover of a windturbine is the load-carrying frame, which is also known to be one of themost critical components of the wind turbine. The load-carrying frametypically consists of a rear frame part, a front frame part, andoptionally a generator frame part, which frame parts are installed inthe nacelle cover to carry and support many of the components andmachinery that transform the wind's kinetic energy conferred to therotor into mechanical energy to turn a generator that produces electricpower. The components and machinery are hitherto installed on theload-carrying frame, which is then lifted into the nacelle cover,secured to the nacelle cover and aligned with the rotor to be put inoperative condition to gain electric power. The front frame part and theoptional general frame part may be referred to as the bed plate frameand the rear frame part may be referred to as the main frame.

The load-carrying frame is typically a cast steel frame or a steel framebolted together, and thus very heavy, and expensive to manufacture.Moreover, said load-carrying frame must be subjected to expensivequality controls and non-destructive testings. The load-carrying frameare also expensive, strenuous, and time-consuming to transport to theerection site, as well as to lift into the nacelle cover with thecomponents and machinery supported on the load-carrying frame, as dealtwith in U.S. Pat. No. 7,793,964 B2 and European patent application no.EP 3 246 561 A1, respectively.

In a typical wind turbine, the hub is secured to the front of thenacelle cover with the blades directly bolted to the hub, or bolted tothe hub via a pitch bearing. The yaw system, mainshaft bearing, gearbox,generator, transformer and electrical control cabinets are behind thehub and conventionally mounted on the front frame of the nacelle.

The load-carrying frame can e.g. be made as two heavy main cast and/orwelded steel parts, wherein e.g. the yaw system, main shaft, andoptionally the gearbox, are secured to the front frame part, and thetransformer, and electrical cabinets are secured to the rear frame part.The generator can conventionally be secured to any of the front framepart and the rear frame part. Once the yaw system passes its rotationaltest and its motors are installed and pass their functional tests, thefront frame part and rear frame part are joined by heavy bolts. Theentire load-carrying frame assembly with its machinery and othercomponents is then attached by brackets to the walls of thefiber-reinforced composite nacelle cover.

European patent application no. EP 2 322 795 A2 describes an example ofa load-carrying frame installed in a nacelle cover.

A load-carrying frame is thus disposed within the nacelle cover to carryand support the main machinery components of the wind turbine using aplurality of brackets mounted at an upper and a lower portion of theload-carrying frame to secure the load-carrying frame to the nacelleinner.

The wind industry is always in demand of ways to reduce productionscosts and to improve the ways a wind turbine is produced, so it is amain aspect of the present invention to reduce productions costs of awind turbine.

SUMMARY OF THE INVENTION

In yet an aspect is provided a wind turbine, for which the amount ofsteel for manufacturing the load-carrying frame can be reduced.

In yet an aspect is provided a nacelle having a substantially smaller,typically substantially shorter load-carrying frame than the interiorlength of the composite nacelle cover.

In yet an aspect is provided a nacelle, which is less heavy thanhitherto known.

In one aspect, the present invention provides a nacelle cover for a windturbine, wherein the nacelle cover comprises a roof, opposite sidewallsand a floor assembled together to form a composite material elongatehousing defining an interior space for containing machinery componentsof the wind turbine, the housing having a front end for mounting to atower of the wind turbine, and an opposite rear end, wherein each of theroof, the opposite sidewalls and the floor comprises a fibre-reinforcedpolymer composite material, characterised in that at least one machinerycomponent of the wind turbine is mounted on the housing at a positionlaterally spaced from the tower in a longitudinal direction along thehousing, and the housing comprises a structural tube which functions asa vertically displaceable cantilever beam carrying the load of the atleast one machinery component mounted thereon, wherein in an unloadedstate prior to mounting the at least one machinery component on thehousing, the rear end is higher than the front end, and in a loadedstate after mounting the at least one machinery component on thehousing, the rear end is lowered as compared to the unloaded state byflexural elastic deformation of the structural tube.

Preferred or optional features are defined in dependent claims 2 to 18.

Also disclosed herein as another aspect of the present invention is acomposite nacelle cover which has a composite wall constituting a firstload-carrying structure for at least one component of a first part ofmain machinery components of the wind turbine, preferably for severalcomponents of the first part of main machinery components, andpreferably all components of the first part of main machinerycomponents.

Thus at least some of the machinery and operative components of the windturbine that converts the kinetic energy of the wind into electricalpower are installed inside the composite nacelle cover by being secureddirectly to the composite wall of the composite nacelle cover, e.g. bymeans of brackets and bolts, without said first part of main machinerycomponents are supported on a load-carrying frame. Instead such firstpart of main machinery components can be secured directly to thecomposite wall of the composite nacelle cover at selected securingpoints and locations. In other words the composite nacelle cover has atleast one main machinery component secured to the composite wall of saidcomposite nacelle cover instead of to a load-carrying frame.

Within the scope of the present invention the term “nacelle cover” isunderstood to mean the part of the wind turbine that houses the mainmachinery, and to which the rotor are mounted at a front end. Typicallythe composite nacelle cover has a bottom hole that is aligned with ahole in a bed plate at the top of the tower.

Within the scope of the present invention the term “composite” means amade from two or more constituent materials with significantly differentphysical or chemical properties that, when combined, produce a materialwith characteristics different from the individual components. The“composite” preferably include a polymer matrix reinforced with fibers.Fibre-reinforced polymers may be thermosettings, e.g.carbon-fibre-reinforced polymer (CFRP) and glass-reinforced plastic(GRP). The plastic composite may be used in a laminate having a core,such a foam core, e.g. a polyurethane foam core of a honeycombstructure, sandwiched between opposite composite face skins, therebyproviding thickness and structural strength to the laminate, and thus toa wall of a composite nacelle cover made of such laminate.

Within the scope of the present invention the term “bed plate” or “bedplate frame” means the transition piece of the load-carrying framelocated inside the composite nacelle cover and connecting the mainbearing(s), the shafts, the generator, and 30 optionally the gearbox ifpresent, towards the rotor at one side, and the yaw bearing towards thetower on the other side. The terms “bedplate” and “bed plate frame” areused interchangeably in the following description.

Within the scope of the present invention the term “main machinerycomponents”, “main components”, and “machinery” are used interchangeablyfor the components including but not limited to the main support, yawsystem, brakes, cooling system, transformer, computer, electricalcontrol cabinets, and the drive train including the low-speed shaft(main shaft), the gearbox, the high-speed shaft, shaft bearings, and thegenerator.

By securing some of the main machinery components to the composite wallof the composite nacelle cover, e.g. to the floor and/or sides of thecomposite nacelle cover, instead of to a load-carrying frame, a lot ofheavy steel for manufacturing said load-carrying frame can be dispensedwith, as well as costs and many man-hours for testing the conventionallylong load-carrying frame can be saved.

Some manufactures may however choose to still use a part of aload-carrying frame for supporting at least one component of a secondpart of the main machinery components of the wind turbine, which part ofthe load-carrying frame may constitutes a second load-carrying structurefor the main machinery components not being secured to the compositewall of the composite nacelle cover. It is however preferred to supportas few components of the second part of the main machinery components aspossible on the load-carrying frame, and instead utilize the compositenacelle cover wall as the load-carrying structure.

The composite nacelle cover can be a fiber-reinforced composite nacellecover, preferably a fiber-reinforced composite nacelle cover havingopposite plastic face skins laminating a foam core. The fiber-reinforcedcomposite may e.g. be glass fibers/epoxy matrix composites, naturalcomposites, hybrid and nanoengineered composites, and e.g. any of thecomposites described in the article “Materials for Wind Turbine Blades:An Overview”, by Leon Mishnaevsky, Jr., Kim Branner, Helga NorgaardPetersen, Justine Beauson, Malcolm McGugan, and Bent F. Sorensenpublished in Materials Oct. 13, 2017. Fiber reinforcement increases thestrength of the plastic by acting as a stress dissipater. When theplastic, the polymer, is subjected to stress forces the energy istransferred to the stronger reinforcing fibers embedded within theplastic matrix. The fibers transmit the stress over a wider physicalarea or throughout the entire plastic skin.

Metal nacelle covers are explicitly excluded, and do not form part ofthe present invention. Drilling holes for brackets for securing of mainmachinery components in a metal nacelle wall provides a basis and a pathfor rust formations and corrosive attack due to humid always present inthe surroundings. Expensive precautionary provisions, actions andprocesses are required to avoid these consequences, such as additionalpost processes, such as painting and frequent shifting of many bolts andbrackets, as well as extra surveillance to observe consequences early.Thus metal nacelle covers are not appropriate for the present invention.

The part of the load-carrying frame that constitutes the secondload-carrying structure can be at least a part of a front frame of themain frame, or be the entire front frame, thus the entire bed plate, inwhich cases the second part of the main machinery components may includemachinery components selected from the group comprising one or moremachinery components of the drive train, optionally also the yaw systemor a part of the yaw system. Thus even the length of the front frame canbe reduced compared to conventional front frames, and still providesufficiently safe and strong support, as just a part of the entireload-carrying structure, still keeping e.g. the drive train properlyaligned.

Emphasize is added that for some composite nacelle covers no rear frameis needed at all, optionally no front frame will be needed either, inthat the wall of the composite nacelle cover may be the soleload-carrying structure.

The composite nacelle cover described in the applicant's ownInternational patent application no. WO2019/034214 is particularlysuited for use as load-carrying structure for the main machinerycomponents. This only composite nacelle cover can accommodate a reducedsize load-carrying frame or no load-carrying frame at all.

International patent application no. WO2019/034214 describes a scalablemodular nacelle assembly structure comprised of standard size panelsub-elements of fiber-reinforced composite laminate. These standard sizepanel sub-elements are preferably sections cut from elongate compositelaminate sheet panels having coupling profiles to join to similarlyobtained adjacent panel sub-elements, e.g. joined side by side. Thepanel sub-elements can in the alternative be molded as individualsubcomponents. The surrounding wall of the fiber-reinforced compositenacelle is assembled without using a supporting framework or skeletonfor securing and supporting the panel sub-elements. The applicant canestablish by way of calculations, and tests will confirm, that a modularnacelle assembly structure assembled of standard panel sub-elements offiber-reinforced composite laminate as defined in International patentapplication no. WO2019/034214 is strong, and optimal useful, as theload-carrying structure for at least a part, and preferably at least themajority, of all of the main machinery components, at no risk that themachinery components displace or disengage the composite wall even underheavy external forces, or without the need for the increased maintenancementioned for the metal nacelle cover. The overlapping coupling profilesof the modular nacelle assembly structure described in Internationalpatent application no. WO2019/034214 defines zones of very highstructural strength and integrity that allows the wall of said nacelleassembly structure itself to constitute the support surface andload-carrying structure for securing main machinery components of thewind turbine without using a load-carrying frame, or just using a partof the conventional load-carrying frame. The composite nacelle cover andthe manufacturing method of panel sub-elements of International patentapplication no. WO2019/034214 is incorporated in full in the presentapplication.

Emphasis is made that the present invention is not limited to be usedwith just the composite nacelle cover described in the applicant's ownInternational patent application no. WO2019/034214. Within the scope ofthe present invention main machinery components can be implemented in amultiplicity of other kinds of composite nacelle covers without using aload-carrying frame, or just using a part of the total length of thenormally used load-carrying frame for said composite nacelle cover. Thepresent invention is suited for both complex and simple compositenacelle cover designs. The present invention may reduce the overalllength of the nacelle, and the nacelle may in the long view be madeshorter due to the invention offers a better utilization of the interiorspace of the composite nacelle cover. This way the invention may saveeven further productions costs for the wind energy industry.

In an initial embodiment the first part of main machinery componentsbeing secured to the first load-carrying structure may be one or more ofthe transformer, the computer and/or the electrical control cabinet(s).

A first part of main machinery components can be lifted separately andfast into the nacelle hollow as individual main machinery component(s),which process of course is less heavy and complicated than when liftingthe combined installation of all main machinery components on aload-carrying frame. Once inside the composite nacelle cover eachcomponent of the first part of main machinery components cansubsequently be secured to the wall of the composite nacelle cover. Thesecond part of the main machinery components of the wind turbine thatmight remain secured to at least a part of the load-carrying frame canbe lifted in conventional manner inside the composite nacelle cover, butthis assembled structure is still much less heavy and easier to liftthan if a fully equipped load-carrying frame is lifted. In conventionalwind turbines all parts of main machinery components are lifted incommon on a load-carrying frame, which put a high demand on the ways theparts must be secured to the load-carrying frame in order not todisplace to any extent at all in relation to each other, or drop off theload-carrying frame during lifting. When fewer parts of main machineryneed to be lifted in common the lifting process is less vulnerable tofailure and wind influences. A separate component of the first part ofmain machinery components only needs to be secured to the load-carryingcomposite nacelle cover wall at few points.

The invention also provides freedom to install individual components onother positions inside the composite nacelle cover than previouslydefined and dictated by the conventional load-carrying frame composed ofboth a bed plate frame and a main frame. Thus the interior positioningarrangement of main machinery components, and the design of saidarrangement, can, provided the mechanical interaction of main machinerycomponents allow it and is not affected or destroyed, be customized andtargeted for each customer and each nacelle design, and easily changedif the demand and possibility arises.

The size of the load-carrying frame can, when used in a compositenacelle cover, be reduced substantially compared to conventionalconfigurations of load-carrying steel frames for conventionally knownwind turbine machinery, this way saving a lot of weight. Thus reducingthe size, in particular the length, of the load-carrying frame, e.g. byelimination of the main frame, does not only save amounts of steel, thetransport costs are also reduced, as well as lifting costs, testingcosts, and work time costs. Furthermore, utilization of the interiorspace of the composite nacelle cover can be optimized and utilized thebest possible way.

In case a load-carrying frame is provided in the composite nacelle coverit is preferred that the length of the load-carrying frame from anacelle front end towards a nacelle rear end is shorter than the lengthof plural serially arranged main machinery components, wherein thenacelle front end is closest to the rotor and the nacelle rear end isfarthest from the rotor.

The load-carrying frame of the composite nacelle cover of the presentinvention may in accordance with the present invention have a frontframe part (a bed plate frame), and only a part of a rear frame part(main frame).

In the alternative the load-carrying frame has no rear frame part at alland the machinery components normally secured to the rear frame part aresecured directly to the wall of the composite nacelle cover.

The front frame part can be a steel structure or be manufactured offiber-reinforced composite.

In a preferred embodiments a main machinery component that is notsupported onto a load-carrying frame part as the load-carrying structurecan simply be secured directly to the wall of the composite nacellecover by means of securing means, such as bolts and brackets, andpreferably secured at wall points being predetermined by calculationsbased on models and tests to be particular strong securing points. Thussecuring main machinery components to the wall of the composite nacellecover provides options for securing said main machinery component.

A 3-Dimensional structure of composite nacelle cover that is especiallyfor carrying the load of the machinery components may have substantiallyflat and straight walls, thus walls without any substantially curving.Optionally such a composite nacelle cover may have a substantiallyrectangular appearance with a substantially square cross-section.

The present invention also relates to a wind turbine comprising a towerand a nacelle at the top of the tower. The wind turbine comprises thecomposite nacelle cover described above and being equipped with mainmachinery components secured to the wall of the composite nacelle coverwithout using a load-carrying frame, including not using one or more ofa part of a front frame, a part of a rear frame, the entire front frame,and/or the entire rear frame thereby substantially reducing overallweight of the nacelle and making the installation of the first part ofmain machinery components fast and easy. The composite nacelle cover maybe secured directly to the top of the tower.

As an example within the scope of the present invention it is intendedto reduce the length of the conventional load-carrying frame by aboutone third. For a main frame weighing about 25 tons about 7 tons of steeland about 300 bolts may be saved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with references tothe accompanying drawing, in which

FIG. 1 is a principle sketch in a perspective side view of aconventional embodiment of a composite nacelle cover provided with afirst embodiment of a load-carrying frame;

FIG. 2 shows the same modified in accordance with the present invention;

FIG. 3 shows the same even further modified in accordance with thepresent invention;

FIG. 4 is a principle sketch in a perspective side view of anotherconventional embodiment of a composite nacelle cover provided with asecond embodiment of a load-carrying frame;

FIG. 5 shows the same modified in accordance with the present invention;

FIG. 6 shows the same even further modified in accordance with thepresent invention;

FIG. 7 shows the embodiment of FIG. 6 with two components of the firstpart of the main machinery components secured to the wall of thecomposite nacelle cover, and not to the load-carrying frame;

FIG. 8 is a schematic perspective side view from above of a nacellecover for a wind turbine in accordance with a further embodiment of thepresent invention;

FIG. 9 is a schematic perspective side view from above of the structuraldesign of the nacelle cover of FIG. 8 ;

FIG. 10 is a schematic cross-section along line A of the nacelle coverof FIG. 8 showing an assembly of wall elements forming a housing of thenacelle cover;

FIGS. 11 a and 11 b are schematic cross-sections along line B ofopposite-sided parts of the roof and sidewalls of the nacelle cover ofFIG. 8 illustrating opposite locating mechanisms between the roof andsidewalls of the nacelle cover;

FIG. 12 is an enlarged schematic cross-sectional perspective view alongline B-B illustrating in greater detail one of the locating mechanismsbetween the roof and a respective sidewall of the nacelle cover shown inFIG. 11 b;

FIG. 13 is a schematic perspective side view from below of a nut foraffixing together flanges of the wall elements of the nacelle cover ofFIG. 8 ;

FIG. 14 is a schematic side view, partly in cross-section, of the nut ofFIG. 13 in a threaded bolt and nut assembly when used or affixingtogether flanges of the wall elements of the nacelle cover of FIG. 8 ;

FIGS. 15, 16 and 17 are, respectively, schematic side views of the inner(B) surface, transverse side edge and outer (A) surface of the wallelement of the nacelle cover of FIG. 8 ;

FIG. 18 is a schematic cross-section through a wall part and an integralstructural beam of the wall element of the nacelle cover of FIG. 8 ;

FIG. 19 is a schematic perspective side view, partly in cross-section,of the inner (B) surface of two of the wall elements of the nacellecover of FIG. 8 which have been fixed together by a method in accordancewith a further embodiment of the present invention;

FIG. 20 is a schematic side view of the outer (A) surface of two of thewall elements as shown in FIG. 19 which have been fixed together by themethod in accordance with the further embodiment of the presentinvention;

FIGS. 21 a and 21 b are schematic perspective views of respectiveopposite ends of a joint between two of the wall elements as shown inFIG. 19 which are being fixed together by the method in accordance withthe further embodiment of the present invention;

FIG. 22 is a schematic side view of a fitting assembly for fitting thenacelle cover of FIG. 8 to a bed plate frame of a wind turbine;

FIG. 23 is a schematic side view of a nacelle cover for a wind turbinein accordance with a further embodiment of the present invention in anunloaded state;

FIG. 24 is a schematic side view showing the nacelle cover of FIG. 23 ina loaded state; and

FIG. 25 is a schematic perspective side view from above and the frontshowing how the nacelle cover of FIG. 23 changes shape and configurationbetween the unloaded and loaded states.

DETAILED DESCRIPTION

In the FIGS. 1-7 a longitudinal side wall of the composite nacelle coverhas been left out only for illustrative purposes.

Emphasis is also added that in the figures the components of the firstpart of the main machinery components are only shown schematically asexamples and that the second part of the main machinery components areleft out. Furthermore no bolts or bracket are shown as the securingmeans in the figures. It is however emphasized that such securing meansare present. The composite nacelle cover shown in figures is embodimentsof composite nacelle cover in accordance with the applicant'sInternational patent application no. WO2019/034214. Other designs ofcomposite nacelle covers are within the scope of the present inventionand the example shown in the figures is not exhaustive of the models andembodiments of composite nacelle covers that can implement and utilizethe present invention. Also the designs of load-carrying frames shown inthe figures are only examples, and load-carrying frames of multipledesigns can be reduced in size, or be manufactured with reduced size forthe purpose of the present invention.

When a main machinery component, whether it being the first part, thesecond part or both said parts, is secured to a sidewall of thecomposite nacelle cover this should not be construed as limiting thescope of the present invention. Such a component could quite as well besecured to the floor, end walls, or even to the roof, although not tothe hatch.

The first embodiment of a composite nacelle cover 1 shown in FIG. 1 is afirst embodiment of a composite nacelle cover in accordance with theapplicant's International patent application no. WO2019/034214 assembledof plural panel-sub elements 2 of fiber-reinforced composite laminate,wherein opposite plastic face skins laminates a foam core. The pluralpanel-sub-elements 2 of fiber-reinforced composite laminate areassembled into flat walls, and thus better suited for suspending ofmachinery components, or any other items, than curved walls.

The composite nacelle cover 1 thus has six flat walls: a floor 3, a roof4, opposite flat sidewalls 5, an inclined front end wall 6, and aninclined rear end wall 6, which walls delimit an interior space 7 foraccommodating a conventional first embodiment of a load-carrying frame 8supporting a first part 9 a;9 b of the main machinery components and asecond part of the main machinery components (not shown, but the generalposition is indicated by reference numeral 10).

The floor 3 has a bottom hole 11 for securing the composite nacellecover 1 in accessible communication with the tower (not shown) of thewind turbine (not shown) to provide access to the nacelle inner from thetower. The yaw system (not shown) of the wind turbine is located in thevicinity of the bottom hole 11.

The inclined front end wall 6 has a front hole 12 for securing the rotor(not shown).

The load-carrying frame 8 has a front frame part 13 terminating in aframe front end 14 and an opposite rear frame part 15 terminating in aframe rear end 16. The load-carrying frame 8 is a steel framework 17 ofvery simple design, in that the steel framework 17 is in the form of alatticework composed of horizontal steel beams 18 and vertical steelbeams 19 defining rows of squares 20 along the walls 3,4,5,6 of thecomposite nacelle cover 1, some of which squares 20 have yet a diagonalsteel beam 21 for further structural reinforcement. The load-carryingframe 8 rests on the floor 3 and is secured at appropriate securingpoints to any of the walls 3,4,5,6 of the composite nacelle cover 1using bolts (not shown) and brackets (not shown).

The first part 9 a;9 b of the main machinery components are illustratedas square boxes, but can typically be a transformer 9 b and anelectrical cabinet 9 a.

The first embodiment of a load-carrying frame 8 has no well-defineddistinction between the front frame part 13 and the rear frame part 15that specifically serves as a distinct bed plate frame and main frame,respectively.

The length of the first embodiment of a load-carrying frame 8 is easilymodified within the scope of the present invention.

In the first modification of the first embodiment of a load-carryingframe 8 seen in FIG. 2 , a fifth of the length of the load-carryingframe 8 seen in FIG. 1 has been eliminated and one machinery component 9a of the first part 9 a;9 b of machinery components has been secured tothe side wall 5 or to the floor 3 instead of to a load-carrying frame 8.The rear frame part 15 has been partly removed.

In the second modification of the first embodiment of a load-carryingframe 8 seen in FIG. 3 , two fifth of the length of the load-carryingframe 8 seen in FIG. 1 has been eliminated and both machinery components9 a;9 b of the first part 9 a;9 b of machinery components are nowsecured to the side wall 5 or to the floor 3 instead of to aload-carrying frame 8. The rear frame part 15 has been fully removed.The side wall 5 or the flow 3 of the composite nacelle cover 1 nowserves as the load-carrying structure and two fifth of the metal for theload-carrying frame has been saved.

The nacelle cover 22 shown in FIGS. 4-7 is a second embodiment of acomposite nacelle cover 1 in accordance with the applicant'sInternational patent application no. WO2019/034214. The secondembodiment of a nacelle cover 22 is substantially identical to firstembodiment of a nacelle cover 1 seen in FIGS. 1-3 and for like partssame reference numerals are used.

The second embodiment of a composite nacelle cover 22 accommodates asecond embodiment of a load-carrying frame 23 that has a front framepart 24 in the form of a bed plate frame 25 to support the drive train(not shown), and an opposite rear frame part 26 in form of a main frame27. The shown second embodiment of a load-carrying frame 23 is known inthe art.

In the first modification of the second embodiment of a load-carryingframe 22 seen in FIG. 5 , about a third of the length of the main frame27 seen in FIG. 4 has been eliminated to allow machinery components ofthe first part of machinery components to be secured to the wall of thecomposite nacelle cover 22 instead of to the main frame 27.

In the second modification of the second embodiment of a load-carryingframe 23 seen in FIG. 6 , the main frame 27 seen in FIG. 4 has beeneliminated in its entirety leaving only the bed plate frame 25, which isintended to support the second part of the main machinery components ofthe wind turbine. Both the drive train and the generator can besupported on the load-carrying bed plate frame 25.

However as seen in FIG. 7 the first part 9 a;9 b of the main machinerycomponents are suspended to the side wall 5 of the nacelle cover 22eliminating the function and use of the main frame 27. A main frame 27conventionally takes up space and this space can either be used forsupporting other equipment of machinery, but the length of the nacellecover can also be shortened. A lot of weight of the overall nacellestructure is also eliminated.

The generator (not shown) may in the alternative be placed directly onthe floor 3 of the composite nacelle covers 1;22 instead of the beingsupported by a load-carrying frame 8;23.

Due to the conventional, traditional practice of using a metalload-carrying frame as an indispensable complete load-carrying structurefor all main machinery components, the applicant attempts any prejudicesagainst utilizing the wall of the composite nacelle cover by a gradualconversion to non-use of load-carrying frame for the main machinerycomponents of a nacelle. Thus a gradual reduction of the length of theload-carrying frame is intended within the scope of the presentinvention, optionally until no load-carrying frame is no longer present.

Referring to FIGS. 8 to 22 , there is illustrated a nacelle cover 100for a wind turbine in accordance with a further embodiment of thepresent invention, and a method of joining wall elements of such anacelle cover 100.

Referring first to FIGS. 8, 9 and 10 , the nacelle cover 100 comprises aroof 101, opposite sidewalls 102, 103 and a floor 104 assembled togetherto form a composite material elongate housing 105 defining an interiorspace 106. As described above for the previous embodiments, the interiorspace 106 in use contains machinery components (not shown) of the windturbine (not shown). For example, in a typical wind turbine, the hub issecured to the front of the nacelle cover 100 with the blades directlybolted to the hub, or bolted to the hub via a pitch bearing. In theembodiment of the present invention, the yaw system, mainshaft bearing,gearbox, generator, transformer and electrical control cabinets arebehind the hub and mounted within the nacelle cover 100.

The housing 105 has a front end 107 for mounting to a tower (not shown)of the wind turbine (not shown), and an opposite rear end 108. Aninclined front end wall 109, preferably flat, has a front hole 110 forsecuring the rotor (not shown) of the wind turbine. A rear end wall 111closes the rear end 108. In the illustrated embodiment the rear end wall111 has two inclined faces forming a convex outer surface but may haveany other desired shape and configuration.

The roof 101 is typically provided with one or more detachable panels112 to enable the panels to be removed temporarily after installation ofthe wind turbine when it is required to replace any of the machinerycomponents mounted within the nacelle cover. It is conventional to use acrane to access the interior space 106 via the roof 101 by removing oneor more detachable panels 112 from the roof 101.

The floor 104 has a bottom hole 113 for securing the nacelle cover 100in accessible communication with the tower (not shown) of the windturbine (not shown) to provide access to the interior space 106 of thenacelle cover 100 from the tower. A yaw system (not shown) of the windturbine is typically located in the vicinity of the bottom hole 113.

Each of the roof 101, the opposite sidewalls 102, 103 and the floor 104comprise a fibre-reinforced polymer composite material. Preferably, eachof the front end wall 109 and the rear end wall 111 also comprise afibre-reinforced polymer composite material.

Each of the roof 101, the opposite sidewalls 102, 103 and the floor 104comprise a respective wall element 114, 115, 116, 117 comprising anassembly of a plurality of panels 118, 119, 120, 121 which have beenjoined together to form an respective elongate row 122, 123, 124, 125 ofpanels. Each panel 118, 119, 120, 121 comprises fibre-reinforced polymercomposite material. Preferably, each of the front end wall 109 and therear end wall 111 also comprise an assembly of a plurality of panelscomprised of a fibre-reinforced polymer composite material.

In the illustrated embodiment, the wall elements 115, 116 of theopposite sidewalls 102, 103 are flat, and consequently the oppositesidewalls 102, 103 are flat. The opposite sidewalls 102, 103 can beassembled from identical flat wall elements 115, 116.

Also, the wall elements 114 of the roof 101 are flat or upwardly bowedabout a radius of curvature within the range of from infinity to 16 m.Consequently, the roof 101 is flat or upwardly bowed. An upwardly bowedsurface assists run-off of rain and sliding of snow from the roof 101 tominimise excess snow loads on the nacelle cover 100 during winterweather conditions. The wall element 117 of the floor 104 is flat, oralternatively downwardly bowed about a radius of curvature within therange of from infinity to 16 m. When the roof 101 and/or floor 104 areflat, the roof 101 and/or floor 104 can be assembled from identical flatwall elements 114, 117 which are also identical to the flat wallelements 115, 116 used for the opposite sidewalls 102, 103. When theroof 101 and floor 104 are bowed, the roof 101 and floor 104 can beassembled from identical bowed wall elements 114, 117.

In accordance with one aspect of the present invention, the front end107 of the housing 105 is mounted on a bed plate frame 420, shown highlyschematically by dashed lines in FIG. 9 . The bed plate frame 420 isaffixed to the tower 122 as is conventional to those skilled in the artof wind turbine manufacture and construction.

The bed plate frame 420 supports at least one part of a drive train 124of the wind turbine, the drive train being shown highly schematically bya box composed of dashed lines in FIG. 9 .

At least one machinery component 125, again shown highly schematicallyby a box composed of dashed lines in FIG. 9 , is mounted on the innersurfaces 126 of the opposed sidewalls 102,102 of the housing 105 at aposition laterally spaced from the bed plate frame 420 in a longitudinaldirection along the housing 105. The at least one machinery component125 is part of, or mechanically and/or electrically connected to, thedrive train 124.

In a typical embodiment of the present invention, the yaw system and themainshaft bearing are mounted on the bed plate frame 420 and thegearbox, generator, transformer and electrical control cabinets mountedto the sidewalls 102, 103 within the nacelle cover 100 as described ingreater detail hereinbelow. However, other arrangements of whichmachinery components are mounted on the bed plate frame 420 and thesidewalls 102, 103 may be employed provided that any additional steelframework, i.e. additional to the nacelle housing 105, for mounting anyof the machinery components is avoided.

In the preferred embodiment of the present invention, the two machinerycomponents that are typically located the furthest rearmost distancefrom the front end 107 of the nacelle housing 105, e.g. the generator127 a of the drive train and the transformer 127 b, are mounted on thesidewalls 102, 103.

The machinery component(s) may be directly mounted on the sidewalls 102,103, using fitting mechanisms between the machinery component(s) and thesidewalls 102, 103. Alternatively, the machinery component(s) may beindirectly mounted on the sidewalls 102, 103, for example by using areinforced area of the floor 104 which is fitted to the sidewalls 102,103, a transverse an additional reinforced interior floor which isfitted to the sidewalls 102, 103, or a transverse support assembly whichis fitted to the sidewalls 102, 103, for example transverse beamsmounted between the sidewalls 102, 103, which is fitted directly to thesidewalls 102, 103, and mounting the machinery component(s) on thereinforced area of the floor 104, additional reinforced interior floor,or support assembly. In each of these constructions, the mass andturning moment load of the machinery component(s) are supported by thesidewalls 102, 103.

The housing 105 comprises a structural tube 128 which functions as avertically displaceable cantilever beam carrying the load of the atleast one machinery component 125 mounted thereon.

The at least one machinery component 125 is directly or indirectlymounted on the sidewalls 102, 103 of the housing 105 and the sidewalls102,103 of the housing 105 directly or indirectly support the load ofthe at least one machinery component 125.

Accordingly, preferably the generator 127 a of the drive train and/orthe transformer 127 b of the wind turbine are directly mounted on thesidewalls 102, 103 of the housing 105 at respective positions along thehousing 105 laterally spaced from the bed plate frame 420 and thesidewalls 102, 103 of the housing 105 directly support the load of thegenerator 127 a and the transformer 127 b at the respective positions.As can be seen from FIG. 9 , typically the transformer 127 b of the windturbine is directly mounted on the sidewalls 102, 103 of the housing 105at the rear end 108 of the housing.

In alternative embodiments, one or more other machinery components, inparticular one or more components of the drive train, are mounteddirectly or indirectly to the sidewalls 102, 103 of the housing 105.

In further alternative embodiments, as shown in FIGS. 4 and 5 , a rearframe part, such as rear frame part 26, may be affixed to the bed plateframe 420 and extends rearwardly of the bed plate frame 420 within thehousing 105. At least one said machinery component of the drive trainmay be mounted on the rear frame part. The weight of the machinerycomponent(s) of the drive train mounted on the rear frame part iscarried by, and transferred to the tower 122 by, the bed plate frame420.

The machinery component(s) 125 that are mounted on the sidewalls 102,103at a position laterally remote from the bed plate frame 420 havesignificant mass, typically a total of at least 1 tonne, and therebyexert a significant turning moment on the structural tube 128 whichfunctions as a cantilever beam to support the load of the combinationresulting from both the mass of the machinery component(s) 125 that aremounted on the sidewalls 102,105 and the mass of the portion of thehousing 105 that is rearward of the tower 122, and in particular the bedplate frame 420 fitted thereto.

Referring to FIG. 10 , the roof 101, opposite sidewalls 102, 103 andfloor 104 are assembled at each longitudinally-extending corner 129,130, 131, 132 of the housing 105 by at least one respective fixingmechanism 140 to form a structural joint 133 at least partially alongthe respective longitudinally-extending corner 129, 130, 131, 132.

As a result of this construction, the opposite sidewalls 102, 103function as opposite load-bearing webs of the vertically displaceablecantilever beam to carry the turning moment load, of the housing 105 andthe at least one machinery component 125 mounted on the housing 105, theturning moment being about the mounting to the bed plate frame 420.Furthermore, at least one or both of the roof 101 and floor 104 functionas a respective flange of the vertically displaceable cantilever beaminterconnecting the opposite load-bearing webs of the verticallydisplaceable cantilever beam. Accordingly, the vertically displaceablecantilever beam functions to support the vertical turning moment load ina manner similar to an I-beam, with the opposite sidewalls 102, 103functioning as opposite load-bearing webs and the roof 101 and/or thefloor 104 functioning as flanges.

The structural tube 128 is thereby configured to resist a vertical loadof at least 500 kN, and a vertical bending moment of at least 3500 kNm,applied to the housing 105 at a position laterally of the mountingbetween the front end 107 of the housing 105 and the bed plate frame 420which is affixed to the tower 122.

In some embodiments, any of the roof 101, sidewalls 102, 103 and floor104 may be provided with large openings covered by removable panelswhich can be temporarily opened to access the interior space 106. Whensuch large openings are provided, the opposite wall element may bereinforced to enable that reinforced element to function as the flangeof the respective cantilever beam. For example, when the roof 101 isprovided with a large openable hatch to enable a crane to removemachinery components from the housing 105, the floor 104 may bereinforced to function as the flange for the vertically displaceablecantilever beam and/or the upper edges of the sidewalls 102, 103 may bereinforced to provide a respective top flange structure for eachsidewall 102, 103.

Correspondingly, the roof 101 and floor 104 function as oppositeload-bearing webs of a horizontally displaceable cantilever beam tocarry a lateral load, for example a wind load and/or a yawing loadapplied to the housing 105 about the mounting to the bed plate frame420. Accordingly, the horizontally displaceable cantilever beamfunctions to support the horizontal turning moment resulting from anapplied lateral wind load in a manner similar to an I-beam, with theroof 101 and floor 104 functioning as opposite load-bearing webs of thehorizontally displaceable cantilever beam and the opposite sidewalls102, 103 functioning as flanges of the horizontally displaceablecantilever beam interconnecting the opposite load-bearing webs of thehorizontally displaceable cantilever beam.

The structural tube 128 is thereby configured to resist a horizontallateral load of at least 100 kN, and a horizontal bending moment of atleast 1200 kNm, applied to the housing at a position laterally of themounting between the front end 107 of the housing 105 and the bed plateframe 420 which is affixed to the tower 122.

Each of the roof 101, the opposite sidewalls 102, 103 and the floor 104comprises a respective wall element 114, 115, 116, 117 having oppositelongitudinal edges 134, 135 extending between the front and rear ends107, 108. The longitudinal edges 134, 135 of adjacent wall elements 114,115, 116, 117 of the housing 105 comprise respective longitudinalflanges 136, 137 which are inwardly inclined relative to the respectivewall element 114, 115, 116, 117.

At each longitudinally-extending corner 129, 130, 131, 132 of thehousing 105, the respective adjacent flanges 136, 137 of the wallelements 114, 115, 116, 117 comprise an outer flange 136 and an innerflange 137 which are affixed together in an overlapping relationship bythe fixing mechanism 140 to form the structural joint 133 along therespective longitudinally-extending corner 129, 130, 131, 132.

Typically the outer and inner flanges overlap by at least 50 mm,preferably at least 70 mm, for example any distance from 70 to 150 mm.

Along opposite edges of the roof 101, the flanges 136 of the roof wallelement 114 form the outer flanges 136 and the flanges of the respectiveopposite sidewall elements 115, 116 form the inner flanges 137.Additionally, along opposite edges of the floor 104, the flanges 137 ofthe floor wall element 117 form the inner flanges 137 and the flanges136 of the respective opposite sidewall elements 102, 103 form the outerflanges 136.

Each of the outer and inner flanges 136, 137 are inclined at an anglewithin the range of from 30 to 60 degrees, optionally 45 degrees, to awall part 142 of the respective wall element 114, 115, 116, 117.

Preferably, the structural joint 133 along each longitudinally-extendingcorner 129, 130, 131, 132 has a shear strength, in a plane parallel tothe respective outer and inner flanges 136, 137, of more than 120 kN/m.

Each wall element 114, 115, 116, 117 comprises the wall part 142comprising, or preferably consisting of, a fibre-reinforced polymercomposite material defining outer and inner surfaces of the wall element114, 115, 116, 117. The flanges 136, 137 of the wall element 114, 115,116, 117 are integral with the wall part 142. Alternatively, the flanges136, 137 of the wall element 114, 115, 116, 117 may be affixed to thewall part 142, for example by an adhesive layer (not shown).

A plurality of parallel structural beams 183 are integrally mouldedwith, or affixed to, the wall part 142 on the inner surface of the wallelement 114, 115, 116, 117, wherein the structural beams 183 extend in adirection orthogonal to the opposite longitudinal edges 134, 135 of thewall element 114, 115, 116, 117.

As shown in FIG. 10 , for each wall element 114, 115, 116, 117, thestructural beams 183 are integrally moulded with, or affixed to, eachflange 137 of the respective wall element 114, 115, 116, 117 which formsan inner flange 137 in the housing 105. In the wall elements 115, 116 ofthe opposite sidewalls 102, 103, the structural beams 183 are integrallymoulded with, or affixed to, the upper flange 137 of the wall element115, 117. In the wall element 116 of the floor 104, the structural beams183 are integrally moulded with, or affixed to, the opposite flanges 137of the wall element 116.

In the preferred embodiment, as shown in FIGS. 13 and 14 , the fixingmechanism 140 comprises a threaded bolt and nut assembly 143. The pairof outer and inner flanges 136, 137 have respectivelongitudinally-extending opposed facing surfaces 138, 139 which define apair of opposed load bearing surfaces of the structural joint 133. Thefixing mechanism 140 comprises a mechanical element 141 which extendsthrough the thickness of the pair of outer and inner flanges 136, 137 atthe pair of opposed load bearing surfaces 138, 139. The bolt 144 extendsthrough the thickness of the pair of outer and inner flanges 136, 137,and a head 145 of the bolt 144, with an optional washer, and the nut 146are on opposite sides of the pair of flanges 136, 137.

However, other fixing mechanisms may alternatively be employed, forexample rivets. Alternatively or in addition, the opposed facingsurfaces 138, 139 may be bonded together by an adhesive layer providedtherebetween. Furthermore, in other embodiments a gasket may be disposedbetween the pair of outer and inner flanges 136, 137.

The embodiment of FIGS. 13 and 14 comprises a particular construction ofthe nut 146 which can be pre-joined to the outer flange 136 and remainsecurely connected thereto in the absence of the bolt 144, whichsimplifies the assembly process of the housing 105 by permitting thefixing mechanism 140 to be installed with access only from the interiorspace 106 of the housing 105.

The nut 146 comprises a head part 147 having a hexagonal outer surfacefor engagement by a wrench, an integral shaft part 148 adjacent to thehead part 147, and a cylindrical blind bore 149 which extendslongitudinally along the shaft part 148. The blind bore 149 has an openend 150 at a free end 151 of the shaft part 148 and a closed end 152within the nut 146, typically within the head part 147. The shaft part148 has an external surface of rotation 153 with a first helical thread154 and the blind bore 149 has an internal cylindrical surface 155 witha second helical thread 156. The first and second helical threads 154,156 have opposite rotational directions.

The external surface of rotation 153 of the shaft part 148 isfrustoconically tapered and reduces in radius in a direction towards thefree end 151. Typically, the frustoconically tapered surface 153 has ataper angle of from 1 to 5 degrees, optionally from 1 to 2 degrees,relative to a longitudinal axis of the shaft part 148.

The external surface 153 of the shaft part 148 is threadably screwed, inone rotational direction, typically an anti-clockwise or reverserotational direction, into one of the outer and inner flanges 136, 137,preferably the outer flange 136, by the first helical thread 154. Thetapered external surface 153 of the shaft part 148 securely fits the nut146 onto the outer flange 136. An adhesive, for example an epoxy resinadhesive, may also be provided between the external surface 153 and theouter flange 136 to enhance the strength and durability of the bond.

The bolt 144 extends through a pre-drilled hole 157 in the pair offlanges 136, 137 from the other of the outer and inner flanges 136, 137and is threadably screwed, in the opposite rotational direction,typically a clockwise or forward rotational direction, into the blindbore 149 to securely affix together the pair of flanges 136, 137.

By providing that the nut 146 is threadably screwed into the outerflange 136 by the first helical thread 154, and the bolt 144 extendsoutwardly through the pair of flanges 136, 137 from the inner flange137, the wall elements comprised of a fibre-reinforced polymer compositematerial can be assembled together, disassembled, and re-assembled, fromthe interior space 106.

In accordance with a further aspect of the present invention, asdescribed with reference to FIGS. 8, 11 and 12 , a locating mechanism isprovided between the wall elements to assist assembly of the housing105.

At the pair of longitudinally-extending corners 129, 130 of the housing105 extending along opposite edges of the roof 101, the flanges 136 ofthe roof wall element 114 and the flanges 137 of the respective oppositesidewall elements 115, 116 comprise a locating mechanism 160 forpositioning the flanges 136, 137 of the roof wall element 114 and theflanges of the respective opposite sidewall elements 115, 116 atrespective predetermined interlocked positions.

The flanges 136 of the roof wall element 114 comprise a first locatingelement 161 and the flanges 137 of the respective opposite sidewallelements 115, 117 comprise a second locating element 162. The first andsecond locating elements 161, 162 are configured to interlock togetherat the predetermined interlocked position.

The first locating element 161 in the roof wall element 114 comprises aprojection 163 and the second locating element 162 in the respectiveopposite sidewall elements 115, 116 comprises a socket 164.Alternatively, the first and second locating elements 161, 162 maycomprise a socket and a projection respectively.

The projection 163 and the socket 164 have complementary inwardlytapering surfaces 165 a, 165 b, 166 a, 166 b whereby the projection 163is configured to self-align towards the predetermined interlockedposition within the socket 164 as the projection 163 and the socket 164are progressively engaged together, i.e. when the roof wall element 114is lowered onto the respective opposite sidewall elements 115, 116.

The projection 163 comprises a first inwardly extending integral part167 of the wall 168 of the outer flange 136 and the socket 164 comprisesa second inwardly extending integral part 169 of the wall 170 of theinner flange 137.

The projection 163 therefore comprises first and secondlongitudinally-extending planar surfaces 1665 a, 165 b which are eachinclined to the outer flange 136 and converge to form alongitudinally-extending outer edge 171 forming a tip 172 of theprojection 163. The socket 164 correspondingly comprises third andfourth longitudinally-extending planar surfaces 166 a, 166 b which areeach inclined to the inner flange 137 and converge to form alongitudinally-extending inner edge 173 forming a lowermost part 174 ofthe socket 164.

The first and second longitudinally-extending planar surfaces 1665 a,165 b are inclined to each other by an obtuse angle, and the third andfourth longitudinally-extending planar surfaces 166 a, 166 b areinclined to each other by the obtuse angle, which is the same angle.

The projection 163 has a pair of opposed transversely-extending endwalls 267 which define the length of the projection 163 extending alongthe longitudinal direction of the nacelle cover 100, and correspondinglythe socket 164 has a pair of opposed transversely-extending end walls(not shown) which define the length of the socket 164. The socket 164 isslightly longer than the projection 163 so that in the predeterminedinterlocked position each end wall 267 of the projection 163 is inwardlyadjacent to a respective end wall of the socket 164. Accordingly, theprojection 163 and the socket 164 longitudinally, and therebyhorizontally, position the roof wall element 114 relative to therespective sidewall element 115, 116 in the predetermined interlockedposition. The projection 163 and the socket 164 typically have a length,extending along the longitudinal direction of the nacelle cover 100, offrom 100 to 150 mm.

In the predetermined interlocked position, the first and thirdlongitudinally-extending planar surfaces 165 a, 166 a are adjacent toeach other, and the second and fourth longitudinally-extending planarsurfaces 165 b, 166 b are adjacent to each other. Additionally, thefirst and third longitudinally-extending planar surfaces 165 a, 166 aare substantially vertically oriented and thereby horizontally positionthe roof wall element 114 relative to the respective sidewall element115, 116. Furthermore, the second and fourth longitudinally-extendingplanar surfaces 165 b, 166 b are substantially horizontally oriented andthereby vertically position the roof wall element 114 relative to therespective sidewall element 115, 116.

Preferably, a plurality of the locating mechanisms 140 are interspacedalong the length of each of the pair of longitudinally-extending corners129, 130 of the housing 105 extending along opposite longitudinal edges134, 135 of the roof 101. Alternatively, along the roof 101 there mayonly be provided a first locating mechanism 140 at the front end 107 ofthe housing 105 and a second locating mechanism 140 at the rear end ofthe housing 105.

Referring to FIGS. 8 and 9 , the opposite sidewalls 102, 103 areprovided with a fibre-reinforced polymer composite materialreinforcement 175 at opposite regions 176 of the sidewalls 102, 103 atwhich the front end 107 of the housing 105 is mounted on the bed plateframe 420.

The reinforcement 175 comprises a reinforced sidewall portion 177 whichconstitutes an integral part of the sidewall 102, 103, and at least oneintegral bracket region 178 which constitutes an integral part of thesidewall 102, 103. The bracket region 178 is disposed within a surfacearea of, and at least partly surrounded by, or wholly surrounded by, therespective reinforced sidewall portion 177.

The reinforced sidewall portion 177 extends from the front end 107 ofthe housing 105 in a direction towards the rear end 108 of the housing105 and defines at least 20% of the length of the respective sidewall102, 103 and extends from the floor 104 of the housing 105 in adirection towards the roof 101 of the housing 105 and defines at least50% of the height of the respective sidewall 102, 103.

Between the reinforced sidewall portion 177 and the rear end 108 of thehousing 105, the opposite sidewalls 102, 103 comprise a respective rearwall portion 180.

A panel 181 for forming the rear wall portion 180 of the sidewalls 102,103 is shown in FIGS. 15 to 17 . FIG. 18 shows a cross-section throughpart of the panel 181. Moreover, the same panel structure is used forthe roof 101 and the floor 104.

As described hereinbelow, a plurality of panels 181 are joined togetheras a row of panels 181 to form, respectively, the wall elements 115,116, 114, 117 of the sidewalls 102, 103, the roof 101 and the floor.Identical panels are used to form the rear wall portions 180, and thesame identical panels may also optionally form the roof 101 and floor104 when the roof and floor are flat, like the sidewalls 102, 103. Ifthe roof 101 and/or floor 104 are curved, then curved panels having asimilar structure are employed for the roof 101 and floor 104, thedifference being the curved shape rather than a planar shape.

The panel structure of the rear wall portions 180 of the sidewalls102,103, the roof 101 and the floor 104 are illustrated in FIGS. 15 to18 . The panel 181 comprises a planar wall part 182 and structural beams183 on the inner surface 184 of the panel 181.

The panel of the reinforcement 175, comprising the reinforced sidewallportion 177 and the bracket region 178, has a similar structure, andcomprises a planar wall part and structural beams on the inner surfaceof the panel, with the modification that the planar reinforced sidewallportion 177, the planar bracket region 178, and the structural beamsextending over the planar reinforced sidewall portion 177 and the planarbracket region 178, are reinforced as compared to the planar wall part182 and structural beams 183.

As shown in FIGS. 15 to 18 , the panel 181 to form the rear wall portion180, and optionally also the roof 101 and the floor 104, comprises thewall part 182 comprising a fibre-reinforced polymer composite material.A plurality of parallel structural beams 183 are integrally moulded withthe wall part 182 on the inner surface 184 of the panel 181.Alternatively, the structural beams 183 may be affixed to the wall part182. The structural beams 183 extend in a direction orthogonal toopposite longitudinal edges 186, 187 of the panel 181, which comprisethe flanges 136, 137. In the housing 105, when the panel 181 is used toform the roof 101, the sidewalls 102, 103, and the floor 104, thelongitudinal edges 186, 187 of the panel 181 extend along a longitudinaldirection of the housing 105.

The wall part 182 comprises, and preferably consists of, thefibre-reinforced polymer composite material.

As shown in FIG. 18 , in the wall part 182 the fibre-reinforced polymercomposite material 188 comprises at least one first layer 189 of biaxialfibrous reinforcement. The first layer 189 biaxial fibrous reinforcementcomprises fibres respectively oriented at an angle within the range offrom +30 to +60 degrees, for example +45 degrees±5 degrees, and withinthe range of from −30 to −60, for example −45 degrees±5 degrees, to alongitudinal direction extending along the longitudinal direction of thepanel 181. Each first layer 189 of biaxial fibrous reinforcementcomprises glass fibres and has a total areal weight of from 1400 to 1800g/m²; the first layer 189 may comprise on or more plies of glass fabric.

The fibre-reinforced polymer composite material 188 further comprises atleast one second layer 190 of fibrous reinforcement laminated on eachside of the at least one first layer 189 of biaxial fibrousreinforcement. The second layer 190 of fibrous reinforcement comprisesbiaxial fibres respectively oriented at an angle of +0 degrees, ±5degrees, and +90 degrees, ±5 degrees, to the longitudinal direction ofthe panel 181. Each second layer 190 of fibrous reinforcement comprisesglass fibres and has an areal weight of from 1250 to 1650 g/m²; thesecond layer 190 may comprise on or more plies of glass fabric.

Typically, one first layer 189 is sandwiched between two second layers190, as shown in FIG. 18 . Preferably, each surface, i.e. the outer “A”surface 191 and the inner “B” surface 192, of the wall part 182 iscoated with a conventional gelcoat layer (not shown).

Typically, the wall part 182 has a total thickness of from 6 to 9 mm.

In the illustrated embodiment, the wall part 182 consists of amultilaminar fibre-reinforced resin matrix composite material, whichprovides the combination of high structural strength and a thin wallstructure. In alternative embodiments, the wall part may consist of asandwich structure, comprising a core layer of cellular material betweenouter and inner plies of the fibre-reinforced resin matrix compositematerial. Such a sandwich panel structure can provide enhancedstructural strength but generally requires a thicker wall structure, forexample a total wall thickness of from 10 to 25 mm.

Referring still to FIG. 18 , the structural beam 183 comprises anelongate body 193 of a cellular core material having a cross-section inthe shape of a trapezium. A lower face 194 of the elongate body 193,defining the larger width of the trapezium, is adjacent to the wall part182. A second fibre-reinforced polymer composite material 195 covers theelongate body 193. The second fibre-reinforced polymer compositematerial 195 is preferably integrally moulded with the fibre-reinforcedpolymer composite material 188 of the wall part 182 thereby to sandwichthe elongate body 193 between the fibre-reinforced polymer compositematerial of the wall part 182 and the second fibre-reinforced polymercomposite material 195. Typically, the elongate body 193 of cellularcore material has a thickness of from 40 to 100 mm.

In an alternative embodiment, the second fibre-reinforced polymercomposite material 195 is adhered by an adhesive layer (not shown) tothe fibre-reinforced polymer composite material 188 of the wall part182.

In another alternative embodiment, the elongate body 193 of cellularcore material is omitted, and a void is present, for example a voidhaving the same shape and configuration as the trapezium. The requiredflexural strength of the structural beam 183 may be achieved with orwithout the presence of a core material between the spaced multilaminarfirst and second fibre-reinforced polymer composite materials 188, 195.

The second fibre-reinforced polymer composite material 195 comprises atleast one layer 196 of unidirectional fibrous reinforcement at leastpartly covering the elongate body 193, or above a void. Theunidirectional fibrous reinforcement typically covers only the upperface 197 of the elongate body 193 or void defining the smaller width ofthe trapezium. The unidirectional fibres extend along the length of thestructural beam 183. Typically, the unidirectional fibrous reinforcementcomprises glass fibres, but other fibres may be used, for examplecarbon, Kevlar, natural fibres such as plant fibres, etc. Typically, theunidirectional fibrous reinforcement comprises a plurality ofunidirectional glass fibre layers having a total areal weight of from2500 to 4000 g/m².

The second fibre-reinforced polymer composite material 195 furthercomprises at least one third layer 198 of fibrous reinforcementtransversely extending over the elongate body 193, or void, andlaminated to the fibre-reinforced polymer composite material 188 of thewall part 182 adjacent to and along opposite transverse sides of theelongate body 193, or void. The third layer 198 of fibrous reinforcementcomprises biaxial fibres respectively oriented at an angle of +0 degreesand +90 degrees to the longitudinal direction of the structural beam183. The third layer 198 of fibrous reinforcement typically comprisesglass fibres and has a total areal weight of from 2500 to 3600 g/m².

Preferably, the outer “B” surface 199 of the structural beam 183 iscoated with a conventional gelcoat layer (not shown).

Typically, the second fibre-reinforced polymer composite material 195covering the elongate body 193, or void, has a total thickness of from 3to 10 mm.

Typically, the combination of the wall part 182 and the structural beam183 has a total thickness of from 60 to 90 mm.

As described above, each of the roof 101 and the floor 104 comprise thesame panel structure as the rear wall portion 180 of the sidewalls 102,103.

Typically, the rear wall portion 180 of the sidewalls 102, 103, andoptionally each of the roof 101 and the floor 104, has an in-plane shearstrength of from 25 to 40 N/mm² and an in-plane compression strength offrom 200 to 250 N/mm². Furthermore, preferably in the rear wall portion180 of the sidewalls 102, 103, and optionally each of the roof 101 andthe floor 104, each structural beam has a shear load strength of greaterthan 5 kN and a bending moment strength of greater than 6 kNm.

Turning again to the reinforcement 175, the layers of the wall part 182as described above and shown in FIG. 18 are preferably also provided inthe reinforced sidewall portion 177 and the bracket region 178, and thereinforced sidewall portion 177 and the bracket region 178 are furtherreinforced as compared to the wall part 182 by laminating additionallayers of fibrous reinforcement to the multilaminar structure of thefirst fibre-reinforced polymer composite material 188.

In addition, the reinforced sidewall portion 177, and optionally thebracket region 178, are overlaid by structural beams that have a similarstructure and arrangement as shown for the structural beams 183 on theinner surface 184 of the panel 181. However, the structural beams mayoptionally be further reinforced as compared to the structural beams 183by laminating additional layers of fibrous reinforcement to themultilaminar structure of the second fibre-reinforced polymer compositematerial 195.

In summary therefore, as compared to the wall part 182, thereinforcement 175 has a further reinforced sidewall portion 177, a stillfurther reinforced bracket region 178, and structural beams over thereinforced sidewall portion 177, and optionally the bracket region 178,which beams may optionally be further reinforced.

The fibre-reinforced polymer composite material of the reinforcedsidewall portion 177 comprises, as compared to the wall part 182, atleast two additional first layers of biaxial fibrous reinforcementcomprising fibres respectively oriented at an angle of +45 degrees, ±5degrees, and −45 degrees, ±5 degrees, and at least one additional secondlayer of fibrous reinforcement comprising biaxial fibres respectivelyoriented at an angle of +0 degrees, ±5 degrees, and +90 degrees, ±5degrees, laminated on a side of the first layer of biaxial fibrousreinforcement. Typically, the first layers of biaxial fibrousreinforcement comprise glass fibres and have a total areal weight offrom 4200 to 5400 g/m², and the second layers of fibrous reinforcementcomprise glass fibres and have an areal weight of from 3750 to 5000g/m². The reinforced sidewall portion 177 typically has a totalthickness of from 10 to 16 mm.

The fibre-reinforced polymer composite material of the bracket region178 comprises, as compared to the reinforced sidewall portion 177, atleast two additional first layers of biaxial fibrous reinforcementcomprising fibres respectively oriented at an angle of +45 degrees, ±5degrees, and −45 degrees, ±5 degrees, and at least one additional secondlayer of fibrous reinforcement comprising biaxial fibres respectivelyoriented at an angle of +0 degrees, ±5 degrees, and +90 degrees, ±5degrees, laminated on a side of the first layer of biaxial fibrousreinforcement. Typically, the first layers of biaxial fibrousreinforcement comprise glass fibres and have a total areal weight offrom 7000 to 9000 g/m², and the second layers of fibrous reinforcementcomprise glass fibres and have an areal weight of from 5000 to 6600g/m². The bracket region 178 typically has a total thickness of from 13to 22 mm.

The reinforcement 175 further comprises a plurality of parallelreinforcing structural beams 200, as shown in FIG. 8 , integrallymoulded with the reinforced sidewall portion 177, and optionally thebracket region 178, on an inner surface of the sidewall 102, 103.Alternatively, the reinforcing structural beams 200 may be affixed tothe reinforced sidewall portion 177, and optionally the bracket region178. The reinforcing structural beams 200 extend in a directionorthogonal to opposite longitudinal edges 134, 135 of the sidewall 102,103.

The reinforcing structural beam 200 has the same structure as thestructural beam 183 as described above, except that optionallyadditional fibrous reinforcement is utilised to further reinforce thebeam 200.

As described above, the bracket region 178 constitutes an integral partof the sidewall 102, 103. As shown in FIGS. 8 and 9 , each sidewall 102,103 is provided with two longitudinally spaced bracket regions 178 whichare located in a lower region 202 of the reinforcement 175 of therespective sidewall 102, 103. The bed plate frame 420 is fitted to thebracket regions 178.

In particular, as shown in FIG. 22 , each sidewall 102, 103 is mountedon a respective metal foundation plate 203 of the bed plate frame 420 bya fitting assembly 204.

The fitting assembly 204 comprises a pair of outer and inner washerplates 205, 206 of metal which sandwich the bracket region 178 of thesidewall 102, 103 therebetween. The foundation plate 203 is disposedadjacent to the inner washer plate 206. A plurality of threaded bolt andnut fittings 207 bolt together the outer washer plate 205, the bracketregion 178 of the sidewall 102, 103, the inner washer plate 206 and thefoundation plate 203. Typically, the outer and inner washer plates areeach adhered to the respective outer and inner surfaces 207, 208 of thebracket region 178 by a respective adhesive layer (not shown).Typically, the outer and inner washer plates 205, 206 are each comprisedof steel having a thickness of from 3 to 50 mm.

Referring to FIGS. 19 and 20 , as generally described above, each wallelement 115, 116, 114, 117 of at least the opposite sidewalls 102, 103and preferably also the roof 101 and the floor 104, comprises a row of aseries of adjacent panels 181 a, 181 b which extends longitudinallyalong the housing 105. The adjacent panels 181 a, 181 b are affixedtogether by a panel structural joint 210 extending along respectivepairs of overlapping edges 211 a, 211 b of the adjacent panels 181 a,181 b.

The pair of overlapping edges 211 a, 211 b of the adjacent panels 181 a,181 b have respective opposed panel facing surfaces 212, 213 extendingtransversely relative to the longitudinal direction of the housing 105.One of the panel facing surfaces 212 comprises at least onetransversely-extending raised portion 214 between a pair oftransversely-extending lower portions 215. The raised portion 214 isfixed against the other of the panel facing surfaces 213. Each lowerportion 215 is spaced from the other of the panel facing surfaces 213 bya respective gap 216. Each gap 216 is filled with a sealant or adhesivecomposition 217. Typically, the raised portion 214 has a width of from10 to 50 mm, for example 35 mm, and the gap 216 has a thickness of from1 to 5 mm, for example 1.5 mm. In the preferred illustrated embodiment,the adjacent panels 181 a, 181 b overlap by a distance of from 50 to 150mm, for example 70 mm.

The raised portion 214 and the region of the other panel facing surface213 against which the raised portion 214 is fixed comprise a pair ofopposed load bearing surfaces 218, 219 of the panel structural joint 210when the pair of overlapping edges 211 a, 211 b are bolted together by abolt extending through the raised portion 214; when the pair ofoverlapping edges 211 a, 211 b are adhered together by an adhesivecomposition 217 in the gap 216, the lower portions 215 and the oppositeregions of the other panel facing surface 213 against which the lowerportions 215 are affixed comprise the pair of opposed load bearingsurfaces 218, 219 of the panel structural joint 210.

With respect to each pair of adjacent panels 181 affixed together by apanel structural joint 210, for a first panel 181 a of the pair ofpanels 181, the overlapping edge 211 a is planar with respect to acentral part 220 a of the respective panel 181 a and has a first joiningsurface 221 which faces inwardly of the housing 105. For a second panel181 b of the pair of panels 181, the overlapping edge 211 b is inwardlyoffset with respect to a central part 220 b of the respective panel 181b and has a second joining surface 222 which faces outwardly of thehousing 105. The first and second joining surfaces 221, 222 are affixedtogether to form the panel structural joint 210. The overlapping edge211 a of the first panel 181 a has an outer surface 223 which is alignedwith an outer surface 224 of the second panel 181 b at a location spacedfrom the panel structural joint 210.

Typically, the panel structural joint 210 has a shear strength, in aplane parallel to the respective overlapping edges 211 a, 211 b, of morethan 60 kN/m.

The flanges 136, 137 may also be connected structurally by a flangestructural joint having the same structure as the panel structural joint210 described above, and manufactured by the method as described below,with the raised and lowered portions extending along the length of theflanges 136, 137. However, as described above, the structural joint 133formed from the outer and inner flanges 136, 137 along eachlongitudinally-extending corner 129, 130, 131, 132 has a shear strength,in a plane parallel to the respective outer and inner flanges 136, 137,of more than 120 kN/m; this enhanced shear strength may be achieved bymechanically bolting or riveting together the outer and inner flanges136, 137 as described hereinabove.

With additional reference to FIGS. 21 a and 21 b , there is nowdescribed a method of joining the adjacent panels 181 comprised offibre-reinforced polymer composite material, as shown in FIGS. 19 and 20, to form a wall element 114, 115, 116, 117. A similar method may beused to connect the flanges 136, 137.

As described above with respect to FIGS. 19 and 20 , a pair of panels181 a, 181 b is provided. The pair of panels 181 a, 181 b is assembledtogether as a row extending along a longitudinal direction, and thelongitudinal edges 186, 187 of the panels 181 a, 181 b are aligned. Thetransversely-extending edges 211 a, 211 b of the panels 181 a, 181 b areoverlapped to provide the pair of opposed panel facing surfaces 212,213, as described above. The raised portion 214 is assembled against theother panel facing surface 213 and each lower portion 215 is spaced fromthe other panel facing surface 213 by a respective gap 216. The raisedportion 214, the lower portions 215 and the gaps 216 a, 216 b extendtransversely along the transversely-extending edges 211 a, 211 b of theassembled panels 181 a, 181 b. Each gap 216 a, 216 b has a firsttransverse side 225 a, 225 b adjacent to the raised portion 214 and anopposite second transverse side 226 a, 226 b remote from the raisedportion 214.

The second transverse side 226 a, 226 b of each gap 216 a, 216 b issealed with a respective elongate sealing element 228 a, 228 b to definean elongate moulding cavity 229. The cavity 229 comprises the gaps 216a, 216 b and has opposite first and second longitudinal ends 230 a, 230b.

The first longitudinal end 230 a is connected by a tube (not shown) to asource of liquid resin (not shown) of a sealant or adhesive composition217. The second longitudinal end 230 b is connected by a tube (notshown) to a source of negative pneumatic pressure (not shown).

A liquid resin is infused into the moulding cavity 229 from the firstlongitudinal end 230 a by application of the negative pneumatic pressureto the second longitudinal end 230 b, thereby to fill the mouldingcavity 229 with the liquid resin. Finally, the liquid resin is allowedto harden, and optionally cure, thereby to form a panel structural joint210 between the pair of panels 181 a, 181 b.

In one embodiment, the liquid resin is an adhesive composition 217 andthe adhesive composition 217 provides the entire bond of the panelstructural joint 210 between the pair of panels 181 a, 181 b.

In another embodiment, the liquid resin is a sealant composition and themethod further comprises the step of inserting a mechanical element,such as a bolt or rivet (not shown), through the thickness of the pairof transverse edges 211 a, 211 b to form the panel structural joint 210between the pair of panels 181 a, 181 b. When such a mechanical elementis employed, a gasket may be disposed between the pair of transverseedges 2111 a, 211 b.

Preferably, during the assembling step the pair of panels 181 a, 181 bare assembled together on a template 231 having a three-dimensionallyshaped surface which is configured to mate complementarily with athree-dimensionally shaped surface of each of the pair of panels 181 a,181 b so that the transversely-extending edges 211 a, 211 b overlap by apredetermined distance along the length of the panel structural joint210.

The method may be used simultaneously to join together more than twopanels 181 in a row so that the entire wall element 114, 115, 116, 117can be assembled from a plurality of panels 181 in a singlemanufacturing operation.

A further embodiment of the nacelle cover of the present invention isillustrated in FIGS. 23 to 25 . FIG. 23 is a side view showing thenacelle cover in an unloaded state; FIG. 24 is a side view showing thenacelle cover in a loaded state; and FIG. 25 is a perspective side viewfrom above and the front showing how the nacelle cover changes shape andconfiguration between the unloaded and loaded states.

In FIGS. 23 to 25 , the changes in shape and configuration between theunloaded and loaded states of the nacelle cover are illustrated in ahighly exaggerated form for clarity of illustration.

The nacelle cover 240, comprising a housing 245, has substantially thesame structure as the embodiment shown in FIG. 8 . As shown in FIG. 9 ,at least one machinery component of the wind turbine is mounted on thehousing 245 at a position laterally spaced from the tower in alongitudinal direction along the housing 245. The housing 245 comprisesa structural tube 242 which functions as a vertically displaceablecantilever beam carrying the load of the at least one machinerycomponent mounted thereon.

In in an unloaded state prior to mounting the at least one machinerycomponent on the housing 245, the rear end 2488 is higher than the frontend 247. In the illustrated embodiment, in the unloaded state thestructural tube 242 is upwardly curved in a direction from the front end247 to the rear end 248. Typically the upward curvature has a radius ofcurvature of at least 2000 m, optionally from 2000 to 20000 m.Typically, the upward curvature is continuous along at least the lengthof the housing 245 which extends laterally from the tower 252.

Typically, in the unloaded state the structural tube 242 of the elongatehousing 245 is upwardly curved from the front end 247 to the rear end248 to define an inversed deflection curve, with a maximum deflection atthe rear end of 0.1 to 1% of the length of the housing 105 which extendslaterally from the tower 122.

In contrast, in a loaded state after mounting the at least one machinerycomponent on the housing 245, which is schematically represented by thearrow L in FIG. 25 , the rear end 248 is lowered as compared to theunloaded state by flexural elastic deformation of the structural tube242. The length of the housing 245 which extends laterally from thetower 252 is deflected downwardly. Typically, in the loaded state thestructural tube 242 is linear. Preferably, in the loaded state thestructural tube 242 is within an angular range of +/−1 degree to thehorizontal.

As described above with respect to the bracket regions 178 shown in FIG.9 , the front end 247 of the housing 245 is mounted to the tower 252 bya plurality of fitting assemblies 204, as shown in FIG. 22 , at bracketregions 278 on the opposite sidewalls 502. For example, the front end247 of the housing 245 is mounted on the bed plate frame 420, as shownin FIG. 9 , which is affixed to the tower 252, the bed plate frame 420supporting at least one part of a drive train of the wind turbine. Inthe unloaded state the fitting assemblies 204 are disposed in a firstrotational position relative to the tower 252 and the fitting assemblies204 rotate downwardly to a second rotational position relative to thetower 252 in the loaded state. Typically, as described herein, thefitting assemblies 204 comprise bolts or pins which define supportpoints on the front end 247 of the housing 245. When the housing 245 isunder a vertical load, the support points rotate, but also an angulardeflection in the sidewalls 502 causes the nacelle cover 240 to rotatedownwardly even when the support points do not rotate.

Typically, as described above with reference to FIG. 9 , the at leastone machinery component is directly or indirectly mounted on thesidewalls 502 of the housing 245 and the sidewalls 502 of the housing245 support the load of the at least one machinery component. Pluralmachinery components may be directly or indirectly mounted on thesidewalls 502 at respective positions along the housing 245 laterallyspaced from the tower 522. The sidewalls 502 support the load of themachinery components at the respective positions.

As described above with reference to FIGS. 8 to 10 , the roof 501,opposite sidewalls 502 and floor 504 are assembled at eachlongitudinally-extending corner of the housing 245 by at least onerespective fixing mechanism to form a structural joint along therespective longitudinally-extending corner. Accordingly, the oppositesidewalls 502 function as opposite load-bearing webs of the verticallydisplaceable cantilever beam to carry the turning moment load, about themounting to the bed plate frame, of the housing 245 and the at least onemachinery component mounted on the housing 245. At least one or both ofthe roof 501 and floor 504 function as flanges of the verticallydisplaceable cantilever beam interconnecting the opposite load-bearingwebs of the vertically displaceable cantilever beam.

In addition, the roof 501 and floor 504 function as oppositeload-bearing webs of a horizontally displaceable cantilever beam tocarry a lateral load, for example a wind load or a yaw load applied tothe housing 245 about the mounting to the bed plate frame. The oppositesidewalls 502 function as flanges of the horizontally displaceablecantilever beam interconnecting the opposite load-bearing webs of thehorizontally displaceable cantilever beam.

1. A nacelle cover for a wind turbine, wherein the nacelle covercomprises a roof, opposite sidewalls and a floor assembled together toform a composite material elongate housing defining an interior spacefor containing machinery components of the wind turbine, the housinghaving a front end for mounting to a tower of the wind turbine, and anopposite rear end, wherein each of the roof, the opposite sidewalls andthe floor comprises a fibre-reinforced polymer composite material,wherein at least one machinery component of the wind turbine is mountedon the housing at a position laterally spaced from the tower in alongitudinal direction along the housing, and the housing comprises astructural tube which functions as a vertically displaceable cantileverbeam carrying the load of the at least one machinery component mountedthereon, wherein in an unloaded state prior to mounting the at least onemachinery component on the housing, the rear end is higher than thefront end, and in a loaded state after mounting the at least onemachinery component on the housing, the rear end is lowered as comparedto the unloaded state by flexural elastic deformation of the structuraltube.
 2. A nacelle cover according to claim 1, wherein in the unloadedstate the structural tube of the elongate housing is upwardly curved ina direction from the front end to the rear end.
 3. A nacelle coveraccording to claim 2, wherein in the unloaded state the structural tubeof the elongate housing is upwardly curved from the front end to therear end about a radius of curvature of at least 2000 m, optionally from2000 to 20000 m.
 4. A nacelle cover according to claim 2, wherein in theunloaded state the structural tube of the elongate housing is upwardlycurved from the front end to the rear end to define an inverseddeflection curve, with a maximum deflection at the rear end of 0.1 to 1%of the length of the housing which extends laterally from the tower. 5.A nacelle cover according to claim 2, wherein the upward curvature iscontinuous along at least the length of the housing which extendslaterally from the tower.
 6. A nacelle cover according to claim 2,wherein in the loaded state the length of the housing which extendslaterally from the tower is deflected downwardly.
 7. A nacelle coveraccording to claim 2, wherein in the loaded state the structural tube ofthe elongate housing is linear.
 8. A nacelle cover according to claim 2,wherein in the loaded state the structural tube of the elongate housingis within an angular range of +/−1 degree to the horizontal.
 9. Anacelle cover according to claim 1, wherein the front end of the housingis mounted to the tower by a plurality of fitting assemblies on theopposite sidewalls, and in the unloaded state the fitting assemblies aredisposed in a first rotational position relative to the tower and thefitting assemblies rotate downwardly to a second rotational positionrelative to the tower in the loaded state.
 10. A nacelle cover accordingto claim 1, wherein the front end of the housing is mounted on a bedplate frame which is affixed to the tower, the bed plate framesupporting at least one part of a drive train of the wind turbine.
 11. Anacelle cover according to claim 1, wherein at least one said machinerycomponent is mounted on a reinforced area of the floor which is fittedto the sidewalls, a transverse reinforced interior floor which is fittedto the sidewalls or a transverse support assembly which is fitted to thesidewalls, and thereby the said machinery component is indirectlymounted on the sidewalls of the housing, and the sidewalls of thehousing indirectly support the load of the said machinery component. 12.A nacelle cover according to claim 1, wherein the least one machinerycomponent comprises at least one or both of a machinery component of thedrive train and a transformer of the wind turbine which are directly orindirectly mounted on the sidewalls of the housing at respectivepositions along the housing laterally spaced from the bed plate frame,and the sidewalls of the housing directly or indirectly support the loadof the machinery component of the drive train and the transformer at therespective positions.
 13. A nacelle cover according to claim 12, whereinat least one or both of the machinery component of the drive train andthe transformer of the wind turbine is or are directly or indirectlymounted on the sidewalls of the housing at the rear end of the housing.14. A nacelle cover according to claim 12, wherein the machinerycomponent of the drive train, which is directly or indirectly mounted onthe sidewalls of the housing at the rear end of the housing, comprisesthe generator.
 15. A nacelle cover according to claim 1, wherein theroof, opposite sidewalls and floor are assembled at eachlongitudinally-extending corner of the housing by at least onerespective fixing mechanism to form a structural joint at leastpartially along the respective longitudinally-extending corner, wherebythe opposite sidewalls function as opposite load-bearing webs of thevertically displaceable cantilever beam to carry the turning momentload, the turning moment being about the mounting to the bed plateframe, of the housing and the at least one machinery component mountedon the housing, and at least one or both of the roof and floor functionas a respective flange of the vertically displaceable cantilever beaminterconnecting the opposite load-bearing webs of the verticallydisplaceable cantilever beam.
 16. A nacelle cover according to claim 15,wherein the roof and floor function as opposite load-bearing webs of ahorizontally displaceable cantilever beam to carry a lateral loadapplied to the housing about the mounting to the bed plate frame, and atleast one or both of the opposite sidewalls function as a respectiveflange of the horizontally displaceable cantilever beam interconnectingthe opposite load-bearing webs of the horizontally displaceablecantilever beam.
 17. A nacelle cover according to claim 1, wherein inthe sidewall, and optionally each of the roof and the floor, has anin-plane shear strength of from 25 to 40 N/mm² and an in-planecompression strength of from 200 to 250 N/mm²
 18. A nacelle coveraccording to claim 1, wherein the structural tube is configured toresist a vertical load of at least 500 kN, and a vertical bending momentof at least 3500 kNm, applied to the housing at a position laterally ofthe mounting between the front end of the housing and the bed plateframe which is affixed to the tower, and/or the structural tube isconfigured to resist a horizontal lateral load of at least 100 kN, and ahorizontal bending moment of at least 1200 kNm, applied to the housingat a position laterally of the mounting between the front end of thehousing and the bed plate frame which is affixed to the tower.